1. Field of the Invention
This invention relates to a microscope apparatus in which a relay optical system is provided and pupil modulation can be produced to observe transparent objects, such as cultured cells.
2. Description of Related Art
Where pupil modulation for phase difference or modulation contrast is produced in a prior art microscope, an annular phase film must be placed in an objective unit. Thus, for example, if a phase-contrast objective lens is used to make a fluorescence observation, fluorescence illumination light and observation light will be absorbed by a modulator and the amounts of light will be decreased. Consequently, the image of a specimen cannot be observed with maximum brightness. Furthermore, if fluorescence and phase-contrast photographs are taken with maximum brightness, a fluorescence objective lens and a phase-contrast objective lens must be provided in replacement of the objective unit in order to prevent attenuation of the amount of light which is attributable to the absorption of light by a phase plate. In this case, it is very difficult to obviate the problem of a position shift in position of a specimen caused by the replacement of the objective unit.
Thus, a pupil projection microscope which provides a pupil modulator in a relay optical system, capable of observing transparent specimens, such as cells, through a bright-field objective lens alone, is proposed by the same applicant as in the present application. This microscope apparatus, as disclosed in Japanese Patent Preliminary Publication No. Sho 60-263918, is designed so that a lens barrel in which a projected pupil image is located can be removed from the body of an inverted microscope, and a phase plate can easily be placed at the position of the projected pupil image.
In addition, as set forth in Japanese Patent Preliminary Publication No. Sho 53-72637 which is also proposed by the same applicant as in the present application, a microscope apparatus is provided in which the pupil of an objective lens is projected in the optical path of a relay lens situated in the body of an inverted microscope and a filter ring element is disposed at the position of this projected pupil. The filter ring element is used by removably mounting an element for phase difference or differential interference.
For a relay optical system for relaying an image without changing magnification, a microscope optical system set forth in Japanese Patent Publication No. Sho 46-2940 is known.
The above-mentioned prior art microscopes, however, have problems which will be described below.
For the pupil projection optical systems used in the conventional inverted microscopes, their specific arrangements are not made clear. Researchers who make actual observations of cells want the use of an objective lens with a low magnification less than 4.times.. In the conventional microscopes, however, pupil modulation for phase difference has usually been produced by an objective lens with a magnification of 4.times. or more. It is for this reason that since the objective lens with a low magnification less than 4.times. has a long focal length, the pupil position is located on the image side of the mounting position of the objective lens, and the pupil modulator which must be situated in the unit of the objective lens is placed out of it to prevent the production of pupil modulation. It is impossible for the conventional inverted microscopes that pupil modulation be produced by the objective lens with a magnification less than 4.times..
In the inverted microscope disclosed in Sho 60-263918 mentioned above, the front lens unit of an imaging lens is disposed adjacent to an objective lens, and thereby rays of light emerging from the objective lens are changed into parallel beams. It is therefore considered that this microscope is intended to use the objective lens for finite distance. Thus, where an up-light microscope uses an objective lens for infinite distance, this objective lens cannot be used in the inverted microscope. Moreover, because the front lens unit of the imaging lens is disposed adjacent to the objective lens, a Nomarski prism of the objective lens for infinite distance cannot be used in the up-light microscope. If the objective lens for finite distance must be used, it is required that the imaging lens be constructed with two lens units. This leads to a high lens cost. Also, although the lens barrel is designed to be removable, an image relay lens (an imaging lens for forming an image at the image plane of an eyepiece) is incorporated in the microscope body and the distance between the imaging lens and the image relay lens is made to be invariable, with the result that the position of the eyepoint cannot be arbitrarily changed. As such, persons with various figures cannot observe images in comfortable positions.
The microscope apparatus set forth in Sho 53-72637 is an inverted microscope with an image magnification of 1.times. and a pupil magnification of 1.times.. This microscope is designed so that the pupil modulator, such as a phase plate or a prism for differential interference, can be placed at the pupil position in the microscope body. Such a microscope, however, uses the objective lens for finite distance and cannot use the objective lens for infinite distance. Furthermore, the specific arrangement of the inverted microscope optical system is not clear.
For an ordinary optical microscope, as disclosed in Sho 46-2940, incident light on an objective lens becomes telecentric, but imaging rays are not. Hence, where an image formed by such an optical system is relayed, aberrations cannot be completely corrected.
In general, an inverted microscope is liable to produce flare and ghost because it has a large number of optical elements and many reflections of an image. Thus, the inverted microscope has recently come to be required in which observation can be made in such a way that the numbers of lens elements and reflecting members constituting the optical system are made as small as possible and flare and ghost caused by detrimental reflected light are reduced to a minimum.
Furthermore, the users of inverted microscopes have been diversified. In recent years, improvements have been required such that various experiments, for example, of membrane potential measurements, can readily be performed, and various observations with phase-contrast and Nomarski microscopes are easily made. In addition, the users urgently require an inverted microscope in which more than one person can make observations in comfortable positions, namely operability and human engineering are fully considered and more than one person can make observations simultaneously in comfortable positions. For prior art corresponding to this, a microscope disclosed in Japanese Patent Publication No. 7-35986 filed by the same applicant as in the present application is known. However, this prior art article fails to describe the details of an optical system in which several people make observations simultaneously and of an improvement on operation.
The of the inverted microscopes of the prior art are designed to observe a specimen from the lower side. Hence, unlike the up-light microscope capable of observing directly the image of an object, reflecting members or surfaces increase in number because of the relay of the image, and the use of the objective lens creating the image at a finite position requires a negative lens to be incorporated in a revolver so that the image is relayed to infinity. Thus, there are problems that the number of lenses increases and an observation image becomes dark, with the result that flare and ghost are liable to occur.